Use of 3D Acoustic Tag and Scanning Split Beam Hydroacoustic Tracking Techniques for Evaluation of a Waste Water Discharge Plume

As part of a study to assess the thermal impacts of discharge of waste water effluent, a hydroacoustic monitoring study was combined with a concurrent 3D acoustic tag tracking study. In the spring of 2012, fixed aspect, scanning, split-beam hydroacoustic techniques were applied in the Sacramento River, directly downstream of a treated waste water effluent pipe. Hourly estimates were made of fish density, target strength, and direction of movement utilizing two split-beam hydroacoustic transducers scanning a total of 14 different aiming angles. In addition, 298 Chinook salmon smolts and 99 predatory fish were surgically implanted with acoustic tags and released. An area approximately 100 m upstream and 100 m downstream of the discharge were monitored, and the tagged out-migrating Chinook smolts and tagged predator movements were tracked in 3D. The impact of the discharge plume appeared to have little impact on the Chinook smolts’ downstream outmigration. In addition, densities of predators around the discharge pipe were relatively low. Some predation on Chinook smolts was observed, but no predation events occurred in the discharge pipe monitoring area. This was a successful implementation combining fixed location scanning hydroacoustic and 3D acoustic tag tracking techniques.